It has been a long known practice to ventilate attics under gable roofs by the use of soffit ventilators.
Soffit ventilators are perforated or louvered vent openings in the underside (soffit) of the eaves of an overhanging roof. The vents allow fresh ambient air to flow into the attic to equalize interior temperature and pressure with the outside. This equalization inhibits moisture from condensing on insulation and wood roofing materials, prevents build-up of ice dams which could buckle shingles and gutters, and reduces air-conditioning costs when hot attic air is replaced by cooler ambient air.
A soffit ventilator system may work in conjunction with a passive roof vent or with a forced-air fan to provide positive ventilation. As hot stale air is withdrawn through the roof vent by convection, wind suction, and/or forced flow, it is replaced by fresh ambient air through the soffit vents.
Attic floors (ceilings of the space below) in such buildings are generally heavily insulated between the joists, either by strips of fiberglass batt set between the floor joists or by loose fiber or particulate insulation blown into the attic to fill between and cover the joists to depths of six inches or more. To be fully effective, the insulation should cover the entire attic floor, extending out to the sill plate of the exterior side walls. However, it is difficult blow fiber or particulate insulation right up to the sill plate without causing a significant quantity to fall across the plate into the eaves and settle on the soffit. If this material covers the screens or blocks the louvers of the soffit vents, the ventilating airflow may become inadequate.
Batt fiberglass is more easily to control than blown insulation, since it is cut to length from a roll and placed between the joists. However, if the batt height is such that the upper edge extends above the joists and presses against the roof sheathing, the ventilating air from the soffit vents may be blocked from flowing freely along the roof and replacing the attic air. In this situation, more conditioned air from the spaces below the insulated ceiling will be exfiltrated to the attic through holes along plumbing stacks and electrical feed wire to replace the attic air withdrawn through the roof vent. This results in a loss of thermal energy, and can cause deleterious moisture accumulation on attic structures as moisture from the warmer conditioned air condenses on the colder structures.
Further, any outside air flow which passes through the insulation layer enroute to the attic space reduces the insulation effectiveness by a phenomena known in the trade as "wind wash", or the passage of outdoor air through insulation. Fiber and particle insulation depend upon entrapping air within the insulating layer; consequently, when outside air is allowed to flow through the layer, it draws with it thermal energy from the conditioned spaces. Studies in cold climates have shown that wind wash occurs when the soffit air flow is allowed to pass through the insulation at the edges where the exterior side walls meet an insulated ceiling, and is responsible for significant heat loss. Ventilating air flow passing through the insulation layer may also release hazardous dust in the attic space.
Consequently, numerous types of baffles have been proposed to prevent insulation from being blown into the eaves, to provide an open flow channel below the roof sheathing, or to stop wind wash through the insulation. The following U.S. patents are illustrative of the wide variety of such baffles:
______________________________________ U.S. Pat. No. 3,240,144 Lind U.S. Pat. No. 3,972,164 Grange U.S. Pat. No. 4,096,790 Curran U.S. Pat. No. 4,102,092 Ward U.S. Pat. No. 4,189,878 Fitzgerald U.S. Pat. No. 4,222,315 Weirich U.S. Pat. No. 4,214,510 Ward U.S. Pat. No. 4,611,443 Jorgensen et al. U.S. Pat. No. 4,660,463 Bottomore et al. U.S. Pat. No. 4,977,714 Gregory ______________________________________
Such prior art baffles attempt to solve the above problems by providing, in some manner, an unobstructed flow channel from the eaves into the attic space. However, soffit ventilation creates an additional problem in providing an entry point to the attic space by insects, particularly those which seek such spaces for nesting colonies, such as bees and wasps. The mesh of the soffit screens or size of the louvers must be large enough to prevent blockage by accumulated debris, yet openings of this size frequently allow easy ingress to insects. To combat this problem, U.S. Pat. No. 4,762,053 proposes a soffit vent with a replaceable small-mesh filter held in a filter frame over the inner side of the vent. Another approach is suggested in U.S. Pat. No. 4,222,315, wherein helical-rolled paper air conduits are press-fit into a fascia board with screened openings.
An object of this invention is to provide a soffit ventilation system with an air-permeable barrier against insect ingress and against flow blockage by internal insulation.
A further object is to provide an alternative embodiment of the invention which prevents wind wash through the insulation.
A further object is to provide such barrier by structure and material which is easily installed in a building, which is flame resistant, which does not wick, absorb or retain moisture, which does not react to cause decay or damage to the surrounding roofing materials, and which is sufficiently durable in normal environmental conditions that it should not need replacement during the lifetime of the roof.
A further object is to provide such barrier by structure which is easily installed, and which is configured for immediate installation in buildings having attic floor joists which are spaced at either the sixteen or twenty-four inch standard spacing.